Procedurally Generated Texture Scaling based on Surface Curve
You can try using a grayscale image to set the factor of the scale of... heh, the scales. That's an incredibly esoteric thing to say, so here is my setup (please forgive my liberal use of "reroute" nodes, I wanted to fit it all in at a decent resolution);



Which results in this (with the "factor" texture that's used in the above node setup, but you can paint the values however you want);



I'm also including the .blend file;